Induction electric furnace



F. LINNHOFF I I INDUCTION ELECTRIC FURNACE Au yza, 1932 Filed Feb. 20.1930 Patented Aug. 23, 1932 umrao STATESPATENIT orrica mm mm,EBERSWALDE; enmr INDUCTION ELECTRIC FURNACE Application fled February80, 1880, serial Io, 48 11,089, and in Germany February 87, 1999.

' nace in order to improve the efliciency of the furnace. I

A further purpose is to avoid excessive stirrin of the molten bath,especially that notices incoreless induction furnaces operi ating uponnormal or low frequencies, by a speclal construction of the secondarycoil surrounding the bath and by proper shaping of the crucible.

A further purpose is to incline the inductor coil turns to thehorizontal wholly or in part throughout their circumference.

A further purpose is to slope the crucible bottom at an angle to thehorizontal over all or art of its extent.

further pu ose is to use the same slo e for the furnace ttom as thatused for t e turns of the inductor coil.

A further purpose is to use an induction furnace bath of variant deptharound the circumference of the inductor coil.

A further purpose is to use an inductor coil so formed that the verticaldistance from any point on the coil to the surface of the bath will bevariant.

A further pu ose is to heat an induction furnace bath wit only moderatestirring, so

that the slag cover will remain continuous over the surface of the bath,andslag may be removed from above the metal.

' 85 A further pur ose is to avoid excessive exposure due to oiling upof the bath in contact with the gases of the atmosphere by maintainingthe bath more quiescent throu hout operation of the furnace.

4 A rther purpose is to force the molten metal toward the pouring spoutand thereby withdraw slag to that part of the surface of the poolfarthest from the pouring spout.

Further urposes will appear in the specification and in the claims.

In the familiar coreless induction furnace as at present known, boilingup near the centween the primary and secondary current- With coilconstructions as at present known, the boilin up of the surface near thecenter of the bat is so excessive that it is practically impossible toskim ofi slag. Therefore. it is very diflicult to use the furnace.

Several suggestions have previousl been made with a view to improvingthe e ciency of the furnace by increasing the seconda resistance. Forexample, an attempt has been so made to increase the length transversedby the secondary current by increasing the diameter of the bath, or todecrease the cross section of the metal through which the current passesby placing a fireproof refractory struc o5 ture concentric with the wallof the bath.

The increase of the diameter has the disadvantage of decreasing the heatefliciency'of the furnace, as the most desirable shape of the bath, thatin which the height and di-za ameter are equal, can no longer beutilized. The insertion of a fireproof refractory body within thefurnace makes it necessary to heat this additional mass of inertmaterial up to th furnace temperature.

My invention is directed particularly to a coreless induction furnace inwhich the inductor coil is wound in a plane inclined to the axis to thecoil, rather than perpendicular or nearly perpendicular to it. -In the vform of my invention, the angle of inclination will be much greater thanthe" well known angle of winding necessitated b the thickness of theindividual turn and the t ickness of the insulation between adjacentturns.

By analogy to a thread I may refer-to that an le as the pitch angle ofthe inductor coil.

gince the secondary current flows in the same lane as the primarycurrent, but in opposite phase, the current flow in a bath heated by mynovel coil will be in an ellipse whose small diameter is the same as thebath diameter. This arrangement therefore increases the secondaryresistance compared with that in baths encircled by inductor coils ofthe current type.

The decrease of-the secondary current by increasing the secondaryresistance is not 'alone sufiicient to prevent excessive boiling in thecenter of the bath, especially in coreless rial.

10 the bath, and this effect operates to oppose the pinch efiect.

Similarly, the distance from the top of the bath to the top of theinductor coil difiers at different points along the bath circumference.With this construction, the pinch efl'ect will be greatest where thevertical distance between the surface and the top of the inductor coilis greatest, but since at that point the vertical column of metalcounteracting the pinch effect is also greatest, the bath will remaincomparatively quiescent.

On the opposite side of the bath, the metal, instead of being pushedupwardly by the motor effect and the force of gravity, will be repelledtoward a point opposite the bottom of the inductor coil.

As the vertical metal column is of greatest height and weight along thatside-of the furnace where the inductor turns are low (i. a, the down ofthe slope), the movement of the bath will be reduced to such an extentthat the bath surface will be inclined very slightly and will slopeupwards from the side at which the inductor coil is highest to the sideat which the inductor coil is lowest. However, the metal at the surfacewill be in constant motion. This motion at the surface of the bath is ofgreat advantage for skimming the slag, while, on the other hand, theundesirable boiling up or eruption of the metal at the surface iseliminated.

In the figures I illustrate a few of the many forms in which myinvention might be embodied, choosing those which are practical andconvenient in operation, and which well illustrate the principle of myinvention. The forms which I show are made diagrammatic for conveniencein pointing out the important features. 1

Figure 1 shows a structure according to my invention, with the supportsfor the crucible sectioned so that the inductor coil and crucible may beseen in side elevation.

Figure 2 corresponds to Figure 1 except as to the shape of the inductorcoil and crucible bottom.

Figure 3 also corresponds generally to Figure 1, but shows a somewhatdifferent inductor coil and crucible bottom.

In the drawing like numerals refer to like parts throughout.

The crucible 1 is shownas supported upon frame structure 2 and iscovered with a lid 3 which may desirably be of refractory matenevaeeoThe crucible may be of any suitable material or of any structureprovided the bottom is made to conform to the structure hereindisclosed.

. About the crucible is placed an inductor coil 4 having the plane ofthe winding inclined rather than perpendicular to the coil axis. Thus,in the form shown the lowest point of the inductor coil is on the sideprovided with the pouring spout 5. While this is desirable, it is not ofcourse necessary in the use of my invention.

In order to avoid stray field losses at the ends of the inductor coils,the furnace is provided with annular segments 6 and 7 of mag neticmaterial. 4

The bottom 8 of the .crucible is inclined, preferably at the same angleas that of the inductor coil winding. \Vith the use of a furnace bottomas shown at 8, the combined action of motor effect and gravity willcause the surface of the liquid bath to assume a shape as shown at 9.The metal is in constant motion from point 10 to point 11, so as to havea constantly changing surface allowing for exposure of the draft to theair without excessive movement of the bath. Reduction of the metal canoccur also without the occurrence of excessive bath movement.

At the point 11 in the crucible it is practical to provide a cavity toallow yielding by the metal at the point of high pressure. Instead ofthis cavity, the spout may be used for this purpose, provided the lowestpoint of the inductor C011 be placed below the spout.

The secondary current runs parallel to the windings of the inductor coil4 and forms ellipses whose small diameters are the same as the internaldiameter of the crucible.

As far a's the construction of the supports for the crucible areconcerned, Figure 2 is the same as Figure 1.' The inductor coil inFigure 2 has a part of each turn inclined with respect to the coil axisand the remainder of each turn p rpendicular to the axis or at a smallpitch angle from the perpendicular with respect to the coil axis. Thuswe see that the portion 12 is substantially perpendicular with respectto the coil axis while the portion 13 is inclined. The bottom 8 of thecrucible is similarly constructed, so that a portion 14 is perpendicularto the coil axis and a portion 15 is inclined thereto.

This arrangement has the advantage of forcing the liquid metal from thecenter of the bath toward the circumference by virtue of the repellingaction of the secondary current of opposite direction, thus obtaining astill greater decrease in the violence of boiling up at the bath center.

Another structure embodying my invention isseen in Figure 3. In thisform the inductor coil turns are inclined to the axis in one directionon one side and in the other direction on the other side of a mid point.

The furnace bottom 8 is somewhat similarly V-shaped in this form.

Thus, considering one inductor coil turn, a sgment 16 slopes to one sidewith respect to the axis of the coil while the segment 17 slopesoppositely. A considerable angle is made between the se cuts 16 and 17.

The repulsion of t e secondar current and the tendency of the metal tobe orced against the walls of the crucible are still more pronounced inthis form.

It will be evident that an advantage of my invention could be gainedwithout using the specific forms shown. For example the individual turnscould be curved instead of straight, and could be inclined according toany law desired, providing that their electric effect upon the bath wasto produce secondary currents generally inclined to the vertical axis ofthe bath rather than perpendicular to the axis.

It will be evident that the molten metal may be given dia onal movementtoward the be higher than that at the op osite side andthat the moltenmetal stream reaking at the surface near the pouring spout will carryslag with it down along the surface toward the far (low) 'side of thesurface of the pool.

In view of my invention and disclosure variations and modifications tomeet individual-whim or particular need will doubtless become evident toothers skilled in the art, to obtain part or all of the benefits ofmyinvention without copying the structure shown, and I, therefore, claimall such in so far as they fall within the reasonable spirit and scopeof my invention.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patents is:

cible containing a metal bath, an inductor coil surrounding the'crucibleand diagonally Y inclined to the vertical axis of the crucible to anextent greater than the pitch of the winding, anda source of current forthe inductor coil.

v 2. In an electric induction furnace,a crucible having a slopingbottom, an inductor coil about the crucible wound in a plane making anangle with the perpendicular to the inductor coil axis substantiallygreater than the pitch angle of the .coil and in the general directionof the bottom slope, and a source of current for the inductor coil.

3. In an electric induction furnace, a crucible, an inductor coil aboutthe crucible in which an individual turn is inclined to the axis of thecoil over part ofits length and perpendicular to the axis of the coilover another art of its length: and a source of current f or the coil.

4. In an electric induction furnace, a crucible, an inductor coil aroundthe crucible in which the planes parallel to the winding of anindividual turn slope more than the pitch of the turns, a source ofcurrent for the coil and a pouring spout for the crucible above thelower, as distinguished from the higher part of the turns.

5. In an electric induction furnace, a crucible, an inductor coilsurrounding the crucible in which the winding of each individual turn issloped, a bottom for the crucible similarly sloped and a pouring spoutat the side of the crucible above the lowest part of the bottom.

6. In an electric induction furnace, a crucible, an inductor coilsurrounding the crucible in which an individual turn has one portion ina plane inclined in generally parallel planes extending in one directionand another portion in a plane inclined in generally parallel planesintersecting the first planes with respect to the coil axis, and asource of current for the coil.

7. In an electric induction furnace, a crucible having its bottominclined to .the horizontal in two directions, an inductor coilsurrounding the crucible having its individual turns similarly inclined'to' the horizontal, and a source of current for the coil.

8. In an electric induction furnace, an inductor coil having two ortionsof its individual turns oppositely inclined to the horizontal, acrucible within the inductor coil having its bottom similarly inclinedfrom a. point, and a source of current for the col 9. In an electricinduction furnace, a crucible adapted to contain a molten charge, a

inductor coil about the crucible whose indi vidual turns vary invertical distances from the horizontal to an extent different from thatdue to their pitches throu hout their lengths, and a source of currentor the coil.

10. In an electric induction furnace, a crucible adapted to contain amolten charge, a.

pouring spout for said crucible and an intop of the coil.

FRANZ LINNHOFF.

ductor coil surrounding the cru ibl d

